Posts Tagged ‘plant ecology’

A Vegetation History

October 11, 2017

My Portal story begins in 1991 when Jim Brown offered me the opportunity to be the Portal postdoc. Among other things, this meant I organized the yearly ant census in which we spent about 2 weeks counting the abundance of ant colonies on the experimental plots. In one of my first summers, I hired Don Sias to help with the census. Don was a non-traditional student and had previously traveled extensively throughout the southwest. One day he mentioned to me that the vegetation in the San Simon valley looked pretty “beat up”. By that he meant the vegetation, dominated by shrubs, had the look of a grassland that had become desertified.

August 2015

I was intrigued by Don’s comment for two reasons. First, Brown and Heske (1990) had recently described a significant increase in grass cover on Portal plots that removed kangaroo rats and mentioned that the site was “near the zone of natural transition from desert to grassland”. Second, while desertification is often associated with overgrazing, Heske and Campbell (1991) found no difference in vegetation across the Portal grazing fence despite 11 years of livestock removal – why hadn’t the grasses recovered with livestock removal if the site had once been a grassland?

When I returned to Albuquerque, I recall asking Jim about the vegetation history of the site. He said that he wasn’t sure and encouraged me to see what I could figure out. That led me to the U.S. General Land Office Surveyors notes. The surveyors described the dominant vegetation they traveled through as each mile-long section line was surveyed. Many, but not all, of the lines near our site were surveyed between 1875 and 1883 and the most common description was “good grass”. However, when the surveyors came back to complete their work in the early part of the 20th century, the descriptions were dominated by the words “scattered shrubs” while grass was not mentioned at all. This change in vegetation coincided with large introductions of livestock into the San Simon valley in the late 1880’s, and then a major drought in the early 1890’s that resulted in tremendous livestock mortality due to starvation.

Our understanding of the recent vegetation change at the site can help to explain the observed shifts in grass cover observed at Portal both over time and across the rodent treatments. It also prompted further investigations into desertification and the role of livestock in affecting soil compaction as a mechanism that helps to explain why reversals of desertification (a recovery of perennial grasses) can require several decades. Finally, it illustrates how careful observations by students and researchers that visit the site can lead to interesting questions and new discoveries.

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I’ve been very fortunate to have worked on the Portal system for almost 30 years. Change seems to be the constant at Portal – you never know what you’ll see and how things have changed since the last visit. This complex system continues to be a source of inspiration as we try to understand it (or, as Morgan says, “unravel her mysteries”).

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14,380

April 19, 2012

The intrepid Portal adventurers counted 14,380 individual plants on 382 sampling quadrats (0.25 m2 each), while also trapping >150 rodents, in only 4 days (March 12-15)! It was a whirlwind trip, but we had a lot of fun and learned a lot about plants! The numbers show Astragalus nuttalianus (Nuttall’s milk vetch, a very small plant) and Erodium cicutarium (Stork’s Bill, a dominant, spreading rosette) to be the most common annuals by far, followed by Lesquerella gordoni (Gordon’s Bladderpod, with pretty yellow flowers), Chaenactis steviodes (Esteve’s pincushion, a fleshy plant with white flowers), and Descurainia pinnata (western tansy mustard, a leggy, inconspicuous mustard).

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Monsoon showers bring summer flowers

October 31, 2011

Last month, September 30-October 5, a group of fellow Portal enthusiasts (Zachary Brym, Katherine Thibault, and Christa Weise) got together at the site to take on not only the rodent survey, but also the summer annual and perennial plant survey. Each experimental plot (50 m X 50 m) also has 16 (0.5 m X 0.5 m) permanent plant sampling quadrats within it so that we can understand what changes might occur in the plant community from year-to-year or based on differences in what rodents might be munching or moving around their seeds. We weren’t sure that we could actually finish the survey between our schedule flights to Arizona, but found that a determined group of (mostly) mammalogists could actually do pretty well at identifying desert plants!

There doesn’t seem to be a great field guide for the plant occurring at the site (barely in Arizona, almost in New Mexico, and a desert transition zone…) but we compiled a small ‘library’ to take out with us including a mini-herbarium of plants pressed over the years, the Flora of New Mexico book, Flora of Arizona Book (Epple), and the Peterson Field Guide to Southwestern and Texas Wildflowers, and a Grasses of Arizona Book. We’d love to hear any suggestions for other guide books for the area, especially for grasses or non-flowering ID characters.

The weather was great and by working all day everyday, we were able to sample all our rodents (still a desert pocket mouse takeover) and get to all the plant quadrates with very few unidentifiable individuals! The area near the Chiricahua mountains seems to have gotten more monsoon rain that many other areas of southeastern Arizona, so there were quite a few plants to count relative to some other years, and I would guess (haven’t finished entering data yet!) that there were about 15 species of annual plants per plot. This is actually relatively high diversity for this site, since many years have less than 5 species present! Most common was the Summer Poppy (Kallstroemia grandiflora), Woolly Tidestromia (Tidestromia lanuginosa), two species of spiderling (Boerhavia intermedia and torreyana) and panicum grass (Panicum arizonicum and hirticaule). We tried to photo document everything identified (and unidentified!) and hope to update our mini-herbarium soon since many of the samples are becoming worse for the wear.

It was a lot of work and a cobbled together fast trip, but we sampled everything and had a lot of fun!

This is a photo of plot 16 showing the vegetation this year. It may look sparse, but its a lot more vegetation than in the last few seasons!

Pit tagging a small desert pocket mouse, Chaetodipus penicllatus.

Kate gets reacquainted with the rodents.

Working on identifying plants in a quadrat, with Christa Weise.

Using the herbarium cards to identify a more rare species this year, Euphorbia micromera.

This is an unidentified carpetweed, Kallstroemia spp. It was really common this year...Any ideas?

Some of the grasses are tricky! We brought back samples of this one, but couldn't decide if it was Eragrostis arid or intermedia. We left the site leaning more towards intermedia.

Zack Brym, Kate Thibault, and Christa Weise work hard on an especially grassy sampling site.

We were lucky to get showers each afternoon to cool things down.